Diagnosing malaria

Microscopic diagnosis

Conventional light microscopy is the established method for the laboratory confirmation of malaria. The careful examination by an expert microscopist of a well prepared and well stained blood film remains currently the "gold standard" for detecting and identifying malaria parasites. In most settings, the procedure consists of: collecting a finger-prick blood sample; preparing a thick blood smear; staining the smear; and examining the smear through a microscope for the presence of malaria parasites.

It is sensitive. When used by skilled and careful technicians, microscopy can detect densities as low as 5–10 parasites per µl of blood (5). Under general field conditions, however, the detection capabilities of a typical microscopist might be more realistically placed at 100 parasites per µl of blood (6).
It is informative. When parasites are found, they can be characterized in terms of their species (P. falciparum, P. vivax, P. ovale, and/or P. malariae) and of the circulating stage (e.g. trophozoites, schizonts, gametocytes). Occasionally, expert microscopists can detect morphological alterations induced by recent drug treatment. In addition, the parasite densities can be quantified (from ratio of parasites per number of leukocytes or erythrocytes). Such quantifications are needed to demonstrate hyperparasitaemia (which may be associated with severe malaria) or to assess parasitological response to chemotherapy.
It is relatively inexpensive. Cost estimates for endemic countries range from about US$ 0.12 to US$ 0.40 per slide examined.¹⁴
It can provide a permanent record (the smears) of the diagnostic findings and be subject to quality control.

It is labour-intensive and time-consuming.
It is exacting and depends absolutely on good techniques, reagents, microscopes and, most importantly, well trained and well supervised technicians. Unfortunately these conditions are often not met, particularly at the more peripheral levels of the health care system. In these circumstances, microscopic diagnosis risks becoming an unreliable tool that uses up scarce resources for doubtful results.
There are often long delays in providing the microscopy results to the clinician, so that decisions on treatment are often taken without the benefit of the results.